1. Field of the Invention
This invention relates to nickel base brazing materials for high temperature applications.
2. Description of the Prior Art
It is well known in the prior art to join nickel base alloys using nickel base brazing compositions. The journal Metal Progress, Apr. 1977, Vol. 112, shows a representative listing of such brazing alloys on page 65. The common feature of such alloys is the use of effective melt depressants such as boron and silicon. Of these, boron is the most effective melt depressant but, homogeneous nickel alloys containing significant amounts of boron are so brittle that they cannot be fabricated into useful shapes and must be used in powder form. U.S. Pat. No. 3,753,794 describes a method for producing ductile nickel boron braze materials. This patent is incorporated herein by reference. The method of the patent involves providing the braze filler alloy in a ductile boron free form, working the ductile alloy into foil form and then adding the required amount of boron by a boriding process. The boriding process produces a thin boron rich surface layer which although extremely brittle, adheres to the ductile substrate even when subjected to minor mechanical strains. However, for many applications, a wire preform is desired and this wire preform is often subjected to severe mechanical strains. Borided wires of diameters greater than about 0.030 inch are found to be subject to spallation of the borided surface layer when strained. Accordingly, it is an object of this invention to provide a ductile nickel boron braze wire material which is not subject to spallation even when subjected to severe bending and melts adequately.